Method of forming a semiconductor device and structure therefor

ABSTRACT

In one embodiment, a control circuit for a linear vibration motor may be configured to drive the linear vibration motor to vibrate using a closed loop run mode followed by an open loop run mode, and may be configured to control the linear vibration motor to stop vibrating using an anti-drive signal wherein the frequency is adjusted to be near to an estimated value of the natural frequency of the linear vibration motor.

PRIORITY CLAIM TO PRIOR PROVISIONAL FILING

This application claims priority to prior filed Provisional ApplicationNo. 62/211,182 entitled “METHOD OF FORMING A SEMICONDUCTOR DEVICE ANDSTRUCTURE THEREFOR” filed on Aug. 28, 2015, and having common inventorTsutomu Murata which is hereby incorporated herein by reference

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to an application entitled “METHOD OFFORMING A SEMICONDUCTOR DEVICE AND STRUCTURE THEREFOR”, Ser. No.15/242,804, having a common assignee, and inventor Tsutomu Murata whichis filed concurrently herewith and which is hereby incorporated hereinby reference.

This application is also related to an application entitled “METHOD OFFORMING A SEMICONDUCTOR DEVICE AND STRUCTURE THEREFOR”, Ser. No.15/242,830, having a common assignee, and inventor Tsutomu Murata whichis filed concurrently herewith and which is hereby incorporated hereinby reference.

BACKGROUND OF THE INVENTION

The present invention relates, in general, to electronics, and moreparticularly, to semiconductors, structures thereof, and methods offorming semiconductor devices.

In the past, the semiconductor industry utilized various methods andstructures to form semiconductor devices to control linear vibrationmotors. In some cases the circuits would drive the linear vibrationmotor to an excessive extent and may cause the weight of the linearvibration motor in the case of the motor. When the weight the case, itoften caused an audible noise and also may have interrupted theoperation of the linear vibration motor. In some cases, the frequency ofthe drive signal used to drive the linear vibration motor may have beendifferent from the frequency for which the linear vibration motor wasdesigned. This could also undesirable audible noise or in some cases mayreduce the effectiveness or efficiency of operation.

Accordingly, it is desirable to have a circuit and/or method thatreduces the occurrence of the weight hitting the case, or that drivesthe linear vibration motor a frequency closer to the design frequency ofthe linear vibration motor, or that provides more efficient operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an example of a portion of anembodiment of a drive control circuit for controlling a linear vibrationmotor (LRA) in accordance with the present invention;

FIG. 2 illustrates in a general manner, a cross-sectional view of anon-limiting example of a linear vibration motor that may be suitablefor use as an LRA for the circuit of FIG. 1 in accordance with thepresent invention;

FIG. 3 is a graph having plots that illustrate some signals that may beformed by the circuit of FIG. 1 in accordance with the presentinvention;

FIG. 4 schematically illustrates an example of a portion of anembodiment of a drive control circuit that may be an alternateembodiment of the circuit of FIG. 1 in accordance with the presentinvention;

FIG. 5 is a graph having plots that illustrate some signals that may beformed by the circuit of FIG. 4 in accordance with the presentinvention;

FIG. 6 schematically illustrates an example of a portion of anembodiment of a circuit that may be an alternate embodiment of a decodercircuit of FIG. 1 or FIG. 4 in accordance with the present invention;and

FIG. 7 illustrates an enlarged plan view of an example of a portion ofan embodiment of a semiconductor device that may include at least one ofthe circuits of FIGS. 1, 4, and/or 6 in accordance with the presentinvention.

For simplicity and clarity of the illustration(s), elements in thefigures are not necessarily to scale, some of the elements may beexaggerated for illustrative purposes, and the same reference numbers indifferent figures denote the same elements, unless stated otherwise.Additionally, descriptions and details of well-known steps and elementsmay be omitted for simplicity of the description. As used herein currentcarrying element or current carrying electrode means an element of adevice that carries current through the device such as a source or adrain of an MOS transistor or an emitter or a collector of a bipolartransistor or a cathode or anode of a diode, and a control element orcontrol electrode means an element of the device that controls currentthrough the device such as a gate of an MOS transistor or a base of abipolar transistor. Additionally, one current carrying element may carrycurrent in one direction through a device, such as carry currententering the device, and a second current carrying element may carrycurrent in an opposite direction through the device, such as carrycurrent leaving the device. Although the devices may be explained hereinas certain N-channel or P-channel devices, or certain N-type or P-typedoped regions, a person of ordinary skill in the art will appreciatethat complementary devices are also possible in accordance with thepresent invention. One of ordinary skill in the art understands that theconductivity type refers to the mechanism through which conductionoccurs such as through conduction of holes or electrons, therefore, thatconductivity type does not refer to the doping concentration but thedoping type, such as P-type or N-type. It will be appreciated by thoseskilled in the art that the words during, while, and when as used hereinrelating to circuit operation are not exact terms that mean an actiontakes place instantly upon an initiating action but that there may besome small but reasonable delay(s), such as various propagation delays,between the reaction that is initiated by the initial action.

Additionally, the term while means that a certain action occurs at leastwithin some portion of a duration of the initiating action. The use ofthe word approximately or substantially means that a value of an elementhas a parameter that is expected to be close to a stated value orposition. However, as is well known in the art there are always minorvariances that prevent the values or positions from being exactly asstated. It is well established in the art that variances of up to atleast ten percent (10%) (and up to twenty percent (20%) for someelements including semiconductor doping concentrations) are reasonablevariances from the ideal goal of exactly as described. When used inreference to a state of a signal, the term “asserted” means an activestate of the signal and the term “negated” means an inactive state ofthe signal. The actual voltage value or logic state (such as a “1” or a“0”) of the signal depends on whether positive or negative logic isused. Thus, asserted can be either a high voltage or a high logic or alow voltage or low logic depending on whether positive or negative logicis used and negated may be either a low voltage or low state or a highvoltage or high logic depending on whether positive or negative logic isused. Herein, a positive logic convention is used, but those skilled inthe art understand that a negative logic convention could also be used.The terms first, second, third and the like in the claims or/and in theDetailed Description of the Drawings, as used in a portion of a name ofan element are used for distinguishing between similar elements and notnecessarily for describing a sequence, either temporally, spatially, inranking or in any other manner. It is to be understood that the terms soused are interchangeable under appropriate circumstances and that theembodiments described herein are capable of operation in other sequencesthan described or illustrated herein. Reference to “one embodiment” or“an embodiment” means that a particular feature, structure orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, appearancesof the phrases “in one embodiment” or “in an embodiment” in variousplaces throughout this specification are not necessarily all referringto the same embodiment, but in some cases it may. Furthermore, theparticular features, structures or characteristics may be combined inany suitable manner, as would be apparent to one of ordinary skill inthe art, in one or more embodiments.

The embodiments illustrated and described hereinafter suitably may haveembodiments and/or may be practiced in the absence of any element whichis not specifically disclosed herein.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an example of an embodiment of aportion of a drive control circuit 100 that may be configured to controla linear vibration motor (LRA) 102. Circuit 100 may receive an supplyvoltage for operating the elements of circuit 100 between a voltageinput 133 and a voltage return 134. Input 133 may be configured toreceive the operating voltage from a power supply and input 134 may beconfigured to connect to the common reference voltage of the powersupply such as for example a ground reference.

FIG. 2 illustrates in a general manner, a cross-sectional view of anon-limiting example of a linear vibration motor that may be suitablefor use as LRA 102 of FIG. 1. The linear vibration motor (LRA) mayinclude a stator and a vibrator and in some embodiments may include aweight. For example, the magnet may be viewed as the stator and themechanism to which the coil is attached may be considered the vibrator.Drive control circuit 100 may be configured to supply a drive current tothe linear vibration motor (LRA) to cause the weight to oscillate up anddown as illustrated by the arrows. Those skilled in the art willappreciate that other linear vibration motors may also be suitable forLRA 102.

Referring back to FIG. 1, drive control circuit 100 may have anembodiment that may include a drive signal generating circuit or drivecircuit 110, a driver circuit 122, an induced voltage detector circuitor detector circuit 130, and a zero cross detection circuit or zerocross circuit 140. Circuit 122 may have an embodiment of an H-Bridgedriver. Drive signal generating circuit 110 have an embodiment that mayinclude a latch circuit 111, a main counter 112, a loop counter 113, adecoder circuit 114, another latch circuit 115, a difference calculatingcircuit or difference circuit 116, another latch circuit 117, a summingcircuit 118, and another latch circuit 119. Circuits 110-111, 114,116-119, and counters 112-113 may have embodiments that receiveoperating power between input 113 and return 134. An embodiment of drivecircuit 114 may be configured to generate a drive signal 121. In someembodiments, drive signal 121 may be formed to cause LRA 102 to vibrate.In response to signal 121, circuit 122 may be configured to form a drivecurrent 123 that may be delivered to LRA 102. Circuit 100 may beconfigured to form current 123 to include a positive polarity of current123 that flows from output 126 through LRA 102 and into output 127, andmay also include a negative polarity of current 123 that flows intooutput 126 from output 127 through LRA 102. Circuit 100 may beconfigured to generate drive current 123 in response to drive signal 121generated by circuit 110 and then supply the thus generated drivecurrent 123 to LRA 102.

FIG. 3 is a graph having a plot 170 that graphically illustrates in ageneralized manner a non-limiting example embodiment of a waveform ofthe BEMF signal, or alternately a signal that may be representative ofthe BEMF signal, formed at output 127 relative to output 126 for a cycle172 of current 123 that may be formed by an embodiment of circuit 100 inresponse to drive signal 121. For example, the plot 170 may be anon-limiting example of an embodiment of a detect signal 131 fromdetector 130. The abscissa indicates time and the ordinate indicatesincreasing value of the illustrated signal.

Assume for example that plot 170 is a signal that swings fromsubstantially a power supply voltage, such as for example a voltageclose to a Vcc voltage, to a voltage that is substantially a commonreturn voltage, such as for example a ground voltage. Also assume thatthere is a center voltage, such as for example a common mode voltage ora reference voltage, substantially centered to the two voltage levels asillustrated by the centerline of plot 170. Thus, the signal of plot 170and the signal that forms plot 170 swings around that center voltage,such as the level illustrated in a general manner by the centerline inplot 170. Since plot 170 and the signal move around this center voltage(Vc), when plot 170 or the signal thereof crosses that center voltage itis regarded as a zero crossing or a substantially zero crossing of thatsignal or of plot 170. Those skilled in the art will appreciate thatother circuits may form the signal that is representative of the BEMFsignal to have other reference voltages other than the common returnvoltage reference and may form the zero crossings at other voltagelevels. For example, the centerline may be substantially a groundvoltage and the signal may signal may swing above and below that groundvalue such as between a positive supply voltage and a negative supplyvoltage. Thus, plot 170 is a general representation of the BEMF signal.

An embodiment of cycle 172 may occur between two negative-to-positivezero crossings of the BEMF signal, such as for example between zerocrossings 177 and 184. An example of cycle 172 begins as thenegative-to-positive transition of the BEMF signal crosses thecenterline such as for example at a zero crossing 177. As used herein,the term “substantially zero crossing” or the term “zero crossing” meansthat the value of the signal may be plus or minus ten percent (10%) ofthe cycle prior to or after the actual zero crossing of the signal. Theplus or minus ten percent means ten percent of the cycle in time oralternately in radians. Additionally, as used herein, the term“substantially zero crossing” has the same meaning of plus or minus tenpercent regardless of any other definition of the word “substantially”that may be used herein. An upwardly sloped portion or positive slopeportion 176 of the BEMF signal illustrates the value of the BEMF signalrising from a negative value toward a positive value, such as forexample after the end of driving LRA 102 with a negative value ofcurrent 123 and before driving LRA 102 with a positive value of current123. The increasing portion of plot 172 after zero crossing 176illustrates that the BEMF signal has a positive value and is becomingmore positive. A substantially horizontal portion 178 of plot 170 thatis above the center line represents an interval in which circuit 100 maydrive LRA 102 with a positive value of current 123. The portion 178results from current 123 flowing into LRA 102. Portions 173 of plot 170illustrates that in some embodiments the BEMF signal formed by LRA 102may not occur while circuit 100 is driving LRA 102, and the portion 174illustrates that the BEMF signal from LRA 102 may return upon circuit100 terminating driving LRA 102. A downwardly sloped portion or negativesloped portion 179 illustrates the value of the BEMF signal aftertermination of driving LRA 102 with the positive value of current 123and before driving LRA 102 with a negative value of current 123. TheBEMF signal is becoming less positive as portion 179 decreases fromportion 178 to a positive-to-negative zero crossing 180, and the BEMFsignal becomes negative for the portion of plot 170 below zero crossing180. A substantially horizontal portion 182 that is below the centerlineillustrates an interval in which circuit 100 may drive LRA 102 with anegative value of current 123. Portion 182 results from circuit 100driving LRA 102 and in some embodiments the BEMF signal from LRA 102 maynot occur during this portion 182. A positive or upwardly sloped portion183 illustrates the value of the BEMF signal after termination ofdriving LRA 102 with the negative value of current 123 and before againdriving LRA 102 with another positive value of current 123. The BEMFsignal is becoming less negative as portion 183 increases from portion182 to zero crossing 184, and the BEMF signal becomes positive for theportion of plot 170 above zero crossing 184. However, cycle 172 ends atzero crossing 184. A cycle of the BEMF signal resulting from current 123may be defined to start and end at different points of the waveform ofthe BEMF signal in other embodiments. Portion 183 may be similar toportion 176.

The sloped portions 176, 179, and 183 of cycle 172 are formed by thevoltage formed by LRA 102 at output 127 relative to output 126. Becausedrive signal 121 is not active for these sloped portions, circuit 100 isnot driving current to LRA 102, thus, circuit 100 may be configured toform the output of circuit 122, or alternately outputs 126 and 127, tohave a high impedance or HiZ for these sloped portions. In anembodiment, circuit 100 may be configured to drive LRA 102 with current123 for portions 178 and 182 of cycle 172, thus a conducting portion ofa cycle, and to not drive LRA 102 with current 123 for the slopedportions of cycle 172, thus, a non-conducting portion of the cycle andthe outputs may have the HiZ for the non-conducting portions. The timeinterval for the non-conducting portion may be referred to as a HiZinterval. As will be seen further hereinafter, those skilled in the artwill appreciate that an embodiment of counter 112 may be configured tocount time intervals of cycle 172 while circuit 100 is forming drivesignal 121 for cycle 172. In one example embodiment, counter 112 may beconfigured to count from 0 to 199 during cycle 172, thereby formingapproximately 200 time intervals for drive signal 121 during cycle 172.Those skilled in the art will appreciate that an embodiment of circuits112 and 113 may be configured to form cycle 172 for current 123. Circuit100 may also have an embodiment wherein circuits 114-118 and theconnections thereto may be configured to estimate the eigen frequencyand to form the adjusted value for the frequency of signal 121.

Referring back to FIG. 1, detector circuit 130, may be configured to beconnected to LRA 102 and detect a difference of electrical potentials atthe both ends of the coil of LRA 102. Circuit 130 may be configured tobe connected to outputs 126 and 127 to receive the BEMF signal formed byLRA 102. Circuit 130 may have an embodiment that may be configured todetect the BEMF signal formed between outputs 126 and 127 by LRA 102during the time interval that circuit 100 is not driving LRA 102 withcurrent 123, thus, the non-conducting portion of the cycle of current123. An embodiment of circuit 130 may be connected to outputs 126 and127 instead of directly to the coil of LRA 102. Circuit 130 may have anembodiment that may form detect signal 131 that may be representative ofthe BEMF signal. An embodiment of circuit 140 may be configured todetect zero crosses of the BEMF signal detected by circuit 130 oralternately to detect zero crossing of signal 131.

An embodiment of circuit 100 or alternately circuit 110 may beconfigured to estimate an eigen frequency for LRA 102 and to control oradjust the drive frequency or frequency of drive signal 121, thus of thefrequency and the time interval or period of a cycle 172, to be as closeto the estimated eigen frequency as possible. Those skilled in the artwill appreciate that the eigen frequency is a natural resonant frequencyof the LRA, and in some embodiments may be the fundamental of thenatural resonant frequency. Circuit 100 may have an embodiment that maybe configured to estimate the eigen function for LRA 102 from a detectedposition of the zero crossing of the back EMF voltage detected bycircuit 140. Circuit 100 may be configured to adaptively vary or controlthe frequency of drive signal 121, thus the frequency of current 123, tobe substantially the same as, or alternately close to, the estimatedeigen frequency of LRA 102. In an embodiment, circuit 100 may beconfigured to adaptively vary or control the frequency of drive signal121 to be no more than one-half of a percent (0.5%) greater than or lessthan the estimated eigen frequency. An embodiment may be configured tovary the frequency of drive signal 121 over a range of plus or minusfifty percent (50%) from a nominal value of the frequency. This functionor method may be referred to as a resonant frequency search method orresonant frequency search mode and a circuit that is configured toperform the method or operate with these functions operates in thismanner may be referred to as a resonant frequency search circuit.Operating in such a manner or method may be referred to as operating ina closed loop run mode.

An embodiment of circuit 110 may also include a register setting circuit135 that may be configured to set an initial or starting value for thefrequency of drive signal 201, thus, set an initial frequency for signal121. For example, in response to circuit 100 being enabled to startforming current 123 to start vibrating LRA 102, circuit 135 may beconfigured to set an initial frequency for signal 121. In an embodiment,circuit 135 may be configured to supply an initial value to circuits 111and 119 as illustrated by the initial value label. Circuit 100 may thenbegin operating in the resonant frequency search mode to form current123, to determine the estimated eigen frequency for LRA 102, and toadjust the frequency of signal 121 to substantially the estimated eigenfrequency. An embodiment of circuit 100 may include that during the HiZinterval of the cycle during the run mode the BEMF signal may beamplified by an amplifier of detector circuit 130 and form signal 131that is representative of the BEMF signal. The amplified signal 131 fromdetector 130 may be received by comparator 141. If the BEMF signal, orthe signal that is representative thereof, crosses the value of thereference signal received by comparator 141, the output of comparator141 changes state. For example, if the BEMF signal is increasing, theoutput of comparator 141 may be asserted in response to the crossing, orif the BEMF signal is decreasing, the output of comparator 141 may benegated in response to the crossing, or alternately vice versa. Detectorcircuit 142 may detect the transitions of the output of comparator 141and form an asserted a detection signal indicating detection of the zerocrossing or substantially zero crossing, and vice versa. Circuit 204 mayuse the detected edges to determine the count of counter 112 anddetermine if the frequency of drive signal 121 needs to increase ordecrease in order to be substantially the same or near to the eigenfrequency of LRA 102. For example, circuit 115 may be configured tolatch the value of counter 112 in response to the asserted state ofcircuit 142. Circuit 116 may be configured to determine the center ofthe latched value and compare that to a center value used for settingcounter 112. The difference may be used to form a new starting value forcounter 112 to change the frequency of signal 121.

Detector 130 may include an embodiment that may be configured toestimate the position of the vibrator portion of LRA 102 by monitoringthe BEMF signal formed by LRA 102 during the non-conducting portion. Asmall value, including a zero value, of the BEMF signal may indicatethat the vibrator is at rest (for example, the vibrator may bepositioned in a maximum reachable point at a south pole side or in amaximum reachable point at a north pole side of LRA 102). Thus, circuit100 may be configured to determine the estimated eigen frequency of LRA102 in such a manner that circuit 140 may be configured to detect thetiming with which the BEMF signal across the coil (such as for examplethe voltage between output 127 relative to output 126) crosses zero andmay also be configured to measure a time interval between the thusdetected zero crosses. The time interval between contiguous zero crossesmay indicate a time interval of a half of a drive cycle of current 123,whereas the time interval between every other zero crossing may indicatea time interval of a full drive cycle of current 123.

Circuit 100 may include an embodiment that may be configured to detectonly the timing with which the BEMF signal across the coil (signalbetween outputs 126 and 127 for example), or alternately signal 131,crosses zero as the BEMF signal is increasing from a negative voltage toa positive voltage during a non-conducting portion of a drive cycle,such as for example for portion 176 or 183 of cycle 172 (FIG. 3). Insuch a case, comparator 141 may be configured to form a negated outputsignal while the BEMF signal is lower than a threshold value, andcomparator 141 may be configured to form an asserted output signal asthe BEMF signal becomes higher than that threshold value or anotherthreshold value. For example, comparator 141 may be configured to form anegated output signal while the output voltage of detector 130 is lowerthan a threshold value, whereas comparator 141 may be configured to forman asserted output signal as the output voltage of detector 130 becomeshigher than a threshold value. The time interval between the assertedand negated values may be used to estimate the eigen frequency of LRA102. For example, detector 130 and circuits 140, 115, and 116 may havean embodiment as a circuit that may be configured to receive the BEMFsignal from LRA 102 and to selectively measure a first frequency of avibration of the linear vibration motor, for example the estimated eigenfrequency. Circuit 110 may be configured to responsively adjust thefrequency or the time interval of the cycle of the next drive signal 121that is used to drive LRA 102. Such operation may be referred to as theclosed loop run mode. Comparator 141 may have an embodiment that isconfigured to operate without hysteresis, or substantially withouthysteresis. Those skilled in the art will understand that there may besome unintentional offset between the inputs to comparator 141 due toprocess tolerances, but these are not considered as forming a hysteresisoperation for comparator 141. Operating substantially without hysteresismay facilitate more accurately detecting the substantially zerocrossing.

Circuit 100 may also include an embodiment that may be configured torepeat the measurement and the adjustment operations for one or morecycles of current 123, such as for example one or more consecutivecycles, so that drive control circuit 100 can continuously drive LRA 102at substantially the estimated eigen frequency or a frequency near tothe estimated eigen frequency of LRA 102. This function or method may bereferred to as the resonant frequency search mode and a circuit that isconfigured to perform the method may be referred to as a resonantfrequency search circuit. Operating in such a manner or method may bereferred to as operating in the closed loop run mode.

In some embodiments, circuit 100 may be configured to operate a brakemode control method and may include associated circuits for controllingand/or performing a brake mode method. This function and relatedcircuits and method may sometimes be referred to as a stop mode ofoperation or a braking mode of operation or a brake mode or a stopcircuit or a brake circuit or braking circuit. For example, in responseto terminating running and driving of LA102, such as a non-limitingexample of terminating operation in the closed loop run mode oralternately stopping to provide positive and negative pulses of current123 to LRA 102 to drive LRA 102 to vibrate or increase vibration,circuit 110 may be configured to control drive signal 121 to form ananti-drive signal that includes forming current 123 as pulses that havea phase that is opposite to the phase of the drive signal used to driveLRA 102 during the closed loop run mode or during an open loop run mode.Those skilled in the art will appreciate that the anti-drive waveform ofcurrent 123 may have an embodiment that may look substantially like thewaveform of cycle 172 of FIG. 3. Operating in the brake mode may includeforming the anti-drive signal with an anti-drive frequency and mayinclude forming a brake mode of an anti-drive current for current 123 tohave a substantially opposite phase such that the substantially oppositephase may also include conducting portions and also non-conductingportions. Circuit 122 may be configured to form a high impedance state,for example a high output impedance during portions of or substantiallyall of the non-conducting portions of anti-drive signal. For the brakemode, circuit 122 may be configured to form the brake mode of current123 with an anti-drive phase that is substantially opposite to the phaseused during the closed loop run mode (or during an open loop run mode)and to supply such brake mode of current 123 to LRA 102. This quickensthe stopping of LRA 102. In some embodiments circuit 122 may beconfigured to vary the amplitude of current 123 proportionally to theamplitude of the BEMF signal received from LRA 102. As the brake mode ofcurrent 123 is applied to the coil of LRA 102, the stator may achieve abraking function to slow or to stop the motion of the vibrator oralternately to slow the speed of the stator. Circuit 100 may also havean embodiment that may be configured to adjust the frequency of theanti-drive signal to be substantially the eigen frequency of LRA 102.Adjusting the frequency of the anti-drive signal assists in reducing theamount of time needed to substantially stop LRA 102 from vibrating.

An embodiment of circuit 100 may be configured to detect that LRA 102 issubstantially no longer moving. For example, circuit 110 may beconfigured to estimate, from the detected BEMF signal, a vibration forceafter the running of the linear vibration motor LRA has terminated (endof closed loop run mode or alternately open loop run mode) and tocontrol the brake mode anti-drive signal of opposite phase based on theestimated vibration force. For a non-limiting example, if the BEMFsignal lies within a predetermined voltage range, circuit 110 may beconfigured to determine that LRA 102 has come to a stop. In other words,it is regarded that the vibration force has become zero or less than apredetermined threshold value. When the above condition has been met,circuit 110 can be configured to stop the supply of the anti-drivesignal to circuit 122. In some embodiments after the criterion has beenmet, the anti-drive signal for half of one full cycle may still besupplied to driver unit 122 before the supply thereof is stopped. Notethat herein, the drive termination of LRA 102 means a normal drive stop(end of closed loop run mode or alternately an open loop run mode)excluding the reverse drive period required for the braking control(brake mode) and the anti-drive signal.

In some situations, the extent of vibration of a linear vibration motormay become too great and may cause the weight to hit the case of theLRA. It has been found that in some cases when the vibration of themotor becomes too great and the weight hits the case, the resonantfrequency search mode may have caused the frequency of the drive signalto be greater than a designed resonant frequency of the linear vibrationmotor. When such occurs, the frequency of the drive signal may be farfrom the design frequency of the linear vibration motor and it may causean undesirable audible noise. In some cases, the higher frequency of thedrive signal can reduce the effectiveness of the operation in the brakemode.

FIG. 4 schematically illustrates an example of an embodiment of aportion of a drive control circuit 200 that is configured to control LRA102. Circuit 200, in some embodiments, may be an alternate embodiment ofcircuit 100 (FIG. 1). Circuit 200 includes a resonant frequency searchcircuit 204. An embodiment of circuit 204 may be configuredsubstantially the same as at least a portion of the resonant frequencysearch circuit of FIG. 1. For example, circuit 204 may, in someembodiments, include circuits 111, 115, 116, 117, 118, and 119, orcircuits that operate substantially similarly, and these circuits may,in some embodiments, be configured in substantially the same manner asin circuit 100. Circuit 204 may be configured to operate the resonantfrequency search mode in a manner substantially similar to the resonantfrequency search operation described in the description of circuit 100in FIG. 1. Circuit 200 may have an embodiment that may be configured tooperate in the closed loop run mode in a manner substantially similar tocircuit 100. Circuit 200 may also have an embodiment that may include anenable (EN) signal 201. In some embodiments, an asserted state of signal201 may allow operation of circuit 200 and a negated state may stopcircuit 200 from forming drive signals or anti-drive signals. Circuit200 may include inputs 133 and 134 (FIG. 1) and receive operating powerin the same manner as circuit 100. Circuit 200 may include an embodimenthaving an amplifier circuit 220 that may be an alternated embodiment ofcircuit 130 of FIG. 1. Circuit 220 may include an amplifier 221 havingresistors 222-225 configured to form a gain circuit for amplifier 221.Amplifier 221 may receive a reference signal or a reference voltage(VREF) 228. In an embodiment, reference voltage 228 may form a voltageor signal at the non-inverting input of amplifier 221 that may besubstantially the voltage Vc of FIG. 3. Reference voltage 228 may have avalue that is referenced to the common return voltage of input 134.

An embodiment of circuit 200 may be configured to have three operatingmodes, the closed loop run mode, an open loop run mode, and a brakemode.

FIG. 5 is a graph having plots that illustrate example embodiments ofsome signals that may be formed by circuit 200 during operation in theclosed loop run mode, the open loop run mode, and the brake mode. Theabscissa indicates time and the ordinate indicates increasing value ofthe illustrate signal. A plot 213 illustrates a non-limiting exampleembodiment of the BEMF signal formed at output 127 relative to output126. Portions 214 illustrate in a general manner a non-limiting exampleof the BEMF signal during the non-conducting portions of current 123.Those skilled in the art will appreciate that the signal may have othervalues for the conducting portion of the cycle as illustrated in generalmanner by other portions of plot 213. Additionally, all of thenon-conducting portions of plot 213 are not labeled for clarity of thedrawings. Those skilled in the art will appreciate that plot 213 hassubstantially the same elements as plot 170 (FIG. 3) but illustratesmore than one cycle of the BEMF signal. A plot 216 is not a signalformed or received by circuit 200 but is an illustration of theintensity of the vibration motion of LRA 102. A plot 217 illustrates oneexample embodiment of current 123 A plot 218 illustrates a non-limitingexample of some possible values of counter 112, and a plot 219illustrates a non-limiting example of some possible conditions of signal211. This description has references to FIGS. 4 and 5.

In an embodiment, circuit 200 may be configured to operate in the samemanner as circuit 100 operates in the closed loop run mode. Thus, in theclosed loop run mode, an embodiment of circuit 200 may be configured toform drive signal 121 at a first frequency and form current 123 at thefirst frequency. Circuit 200 may also be configured to estimate theeigen frequency of LRA 102 and to adjust the first frequency to afrequency that is substantially the estimated eigen frequency or afrequency near to the estimated eigen frequency of LRA 102 in responseto detecting the estimated eigen frequency of LRA 102. Circuit 200 mayinclude an embodiment that operates in the closed loop run mode for afirst number of cycles of drive signal 121, wherein forming drive signal121 includes adjusting the first frequency to a second frequency that isnear to the eigen frequency in response to detecting the eigen frequencyof LRA 102. One non-limiting example of this type of operation isillustrated in FIG. 5 during the operation labeled closed loop. Forexample, an embodiment of circuit 200 may include that during the HiZinterval of the cycle during the run mode the BEMF signal may beamplified by an amplifier 221 and form a signal 226 that isrepresentative of the BEMF signal. In some embodiments, signal 226 maybe substantially similar to or alternately the same as, signal 131 (FIG.1).

Circuit 200 may also include an embodiment that operates in an open looprun mode to drive LRA 102 to vibrate after forming the first number ofdrive cycles of drive signal 121 and current 123 in the close loop runmode. In the open loop run mode, circuit 200 may be configured to formdrive signal 121, and current 123, at a third frequency. The thirdfrequency may be substantially the frequency used for the last cycle ofdrive signal 121 during the closed loop run mode. In another embodiment,circuit 200 may be configured to form the third frequency at a frequencythat is different from the second frequency that was used for the lastcycle in the closed loop run mode. For example, circuit 200 may beconfigured to form the third frequency to be substantially the firstfrequency or some other frequency in other embodiments.

Circuit 200 may be configured to operate at the third frequency for asecond number of cycles of drive signal 121 or of current 123. In theopen loop run mode, an embodiment of circuit 200 may be configured tonot adjust the third frequency and to disable operation of the resonantfrequency search mode. In an embodiment, circuit 200 may be configuredto maintain the third frequency substantially constant during operationin the open loop run mode. Circuit 200 may be configured to maintain thethird frequency substantially constant for the duration of the open looprun mode. In another embodiment, circuit 200 may be configured to changethe frequency of signal 121 and current 123 during the open loop runmode to another frequency but not to the estimated eigen frequency.

Circuit 200 may further include an embodiment wherein circuit 210 may beconfigured to control enabling and disabling circuit 200 from operationwith the resonant frequency search mode. For example, circuit 210 may beconfigured to enable and disable circuit 200 from adjusting thefrequency of drive signal 121 in response to detecting and determiningthe eigen frequency of LRA 102. Circuit 210 may have an embodiment thatmay be configured to inhibit one of or both of detecting or determiningthe estimated eigen frequency. An embodiment of circuit 210 may beconfigured to monitor a value of loop counter 113 to determine thenumber of cycles of drive signal 121 or current 123 that are formed.After forming the first number of cycles in the closed loop run mode,circuit 210 may be configured to assert an ON/OFF control signal 211 tocause circuit 200 to start operation in the open loop run mode. Inresponse to the asserted value of ON/OFF control signal 211, circuit 200may be configured to form drive signal 121 and current 123 at the thirdfrequency and to terminate adjusting the value of drive signal 121.

For example, the ON/OFF signal may be used to inhibit circuit 204 fromreceiving the output of circuit 142 or to selectively force the input tocircuit 204 to a value which inhibits the estimation operation. Circuit200 may include an embodiment in which circuit 210 monitors the value ofloop counter 113 to determine the number of cycles of drive signal 121that are formed in the open loop run mode, and to negate the ON/OFFsignal in response to completing the second number of cycles of drivesignal 121 in the open loop run mode, such as illustrated in FIG. 5 atthe end of the operation labeled “open loop”. In response to completingthe second number of cycles of drive signal 121, circuit 200 may beconfigured to begin operating in the brake mode and forming theanti-drive signal 121 to form the negative phase current signal. Anembodiment may include that circuit 200 may be configured to re-enablethe resonant frequency search mode and to begin adjusting the anti-drivefrequency of drive signal 121 and current 123 to substantially theestimated eigen frequency while operating in the brake mode.

An embodiment may include that circuit 200 may be configured to operatein the brake mode after completing the last cycle of drive signal 121,and/or current 123, in the open loop run mode. Circuit 200 may beconfigured to, when operating in the brake mode, form drive signal 121,and resulting drive current 123, at an anti-drive frequency. Theanti-drive signal may have a cycle substantially the same as cycle 172illustrated in FIG. 3. The anti-drive frequency may be the thirdfrequency and to, when operating in the brake mode, adjust theanti-drive frequency or alternately the third frequency in response todetecting and determining the estimated eigen frequency of LRA 102. Inother embodiments, circuit 200 may be configured to form drive signal121 at a different frequency in response to operating in the brake mode.For example, circuit 200 may begin operating in the brake mode andforming drive signal 121 at the first frequency and to then adjust thefirst frequency in response to detecting and determining the estimatedeigen frequency of LRA 102. Alternately, circuit 200 may be configuredto begin operating in the brake mode and forming drive signal 121 at thesecond frequency or some other frequency, in response to operating inthe brake mode, as long as circuit 200 is configured to adjust the otherfrequency in response to detecting and determining the estimated eigenfrequency of LRA 102. In some embodiments, circuit 200 may be configuredto adjust the anti-drive frequency of signal 121 for each cycle ofsignal 121. Circuit 200 may have a non-limiting example embodimentwherein the operation in the brake mode is substantially the same as thebrake mode operation of circuit 100 except that circuit 200 may beconfigured to use the third frequency to begin operating in the brakemode. An embodiment of circuit 200 may be configured to detect that LRA102 is substantially no longer moving. For example, circuit 204 may beconfigured to estimate, from the detected BEMF signal, a vibration forceafter the running of the linear vibration motor LRA has terminated (endof closed loop run mode or alternately open loop run mode) and toterminate forming the brake mode anti-drive signal based on theestimated vibration force. In another embodiment, circuit 200 may beconfigured to operate in the brake mode for a desired number of cycles.In an embodiment, counter 113 may be configured to count the number ofcycles in the brake mode and assert a signal that is used by circuit 200to terminate forming anti-drive cycles. Adjusting the frequency of thedrive signal when operating in the brake mode may assist in reducing theamount of time required to stop the vibration of LRA 102.

By disabling the resonance frequency search operation, or operating inthe open loop run mode, there is no need to analyze the back EMF voltagefrom the LRA with an analog-to-digital converter and no need to have afunction to adjust the driving voltage with a feedback of vibrationforce. Thus, the size of circuit 200 can be reduced which can reduce thesystem cost. Additionally, even if the drive signal causes the weight ofthe LRA to hit the case, the frequency of the drive signal is stillsubstantially the eigen frequency or very near thereto thus, the brakemode can begin with a drive frequency that is near to the eigenfrequency. Forming brake mode to use substantially the estimated eigenfrequency improves the feel of the system that uses circuit 200.

FIG. 6 schematically illustrates an example of an embodiment of acircuit that may be an alternate embodiment of circuit 114 that isillustrated in FIGS. 1 and 4. Circuit 114 includes a brake controlcircuit or stop control circuit 61 that may be configured to form thehigh impedance state and insert the high impedance period and also maybe configured to assist in forming the anti-drive signals of the brakemode.

FIG. 7 illustrates an enlarged plan view of a portion of an embodimentof a semiconductor device or integrated circuit 900 that is formed on asemiconductor die 901. In an embodiment, any one of circuit 100 or 200may be formed on die 901. Die 901 may also include other circuits thatare not shown in FIG. 7 for simplicity of the drawing. The device orintegrated circuit 901 may be formed on die 901 by semiconductormanufacturing techniques that are well known to those skilled in theart.

Some embodiments described herein may be related to either or both ofU.S. Pat. No. 8,736,201, issued to Tsutomu Murata on May 27, 2014 andU.S. Pat. No. 8,829,843, issued to Tsutomu Murata on September 9, 201,both of which are hereby incorporated herein by reference.

From all the foregoing, one skilled in the art will appreciate that anembodiment of a semiconductor device may include a circuit forcontrolling a linear vibration motor that may comprise:

a first circuit, such as for example circuit 110, configured to form adrive signal (121) to control a frequency of a drive current, such asfor example current 123, through the linear vibration motor;

a second circuit, such as for example circuit 204, configured toselectively measure a first frequency of a vibration of the linearvibration motor;

in an embodiment, the second circuit may have an output coupled to thefirst circuit to provide a frequency signal to the first circuit;

the circuit, such as for example either of circuits 100 or 200,configured to operate in a closed loop run mode and form the drivecurrent at a first frequency and to adjust the first frequency to asecond frequency that is substantially the frequency of the vibration ofthe linear vibration motor in response to a difference between the firstfrequency and the frequency of the vibration of the linear vibrationmotor;

in an embodiment, the circuit may be configured to receive a BEMF signalfrom the linear vibration motor to operate in the closed loop run mode;

the circuit configured to operate in the closed loop run mode for afirst number of cycles of one of the drive current or the drive signal;

In an embodiment, the circuit may include a counter to count the numberof cycles;

the circuit configured to operate in an open loop run mode for a secondnumber of cycles of one of the drive current or the drive signal inresponse to an end of the first number of cycles, the circuit configuredto form the drive current at a substantially fixed frequency for thesecond number of cycles, the drive current having a first phase; and

the circuit configured to operate in a brake mode and to form the drivecurrent with a second phase that is opposite to the first phase inresponse to expiration of the second number of cycles, the circuitconfigured to selectively measure a second frequency of a vibration ofthe linear vibration motor while operating in the brake mode, to formthe drive current with a third frequency and to adjust the thirdfrequency to be substantially the second frequency of the vibration ofthe linear vibration motor.

An embodiment may include that the circuit may be configured toselectively disable the second circuit and to not measure the frequencyof the vibration of the linear vibration motor in response to the end ofthe first number of cycles of the drive current.

In another embodiment, the circuit may be configured to selectivelyenable the second circuit and to measure the frequency of the vibrationof the linear vibration motor in response to the end of the secondnumber of cycles.

The circuit may have an embodiment that may include a counter configuredto count cycles of the drive signal, wherein the circuit is configuredto selectively enable operation in the open loop run mode in response tothe counter counting the first number of cycles.

An embodiment may include that the circuit may be configured toselectively enable operation in the brake mode in response to thecounter counting the second number of cycles. Another embodiment mayinclude that the circuit may be configured to selectively terminateoperation in the brake mode in response to the counter counting a thirdnumber of cycles.

Those skilled in the art will appreciate that a circuit for controllinga linear vibration motor may comprise:

a first circuit, such as for example a circuit 110, configured to form adrive signal to control a frequency of a drive current through thelinear vibration motor to cause a vibration of the linear vibrationmotor, the drive current having a first phase;

a second circuit, such as for example circuit 204 or portions of circuit110, configured to selectively measure a frequency of a vibration of thelinear vibration motor; and

the circuit configured to form the drive current with a first frequencyand a second phase that is opposite to the first phase to slow thevibration of the linear vibration motor, the circuit configured toselectively enable the second circuit to measure the frequency of thevibration of the linear vibration motor and to adjust the firstfrequency to a third frequency that is substantially the frequency ofthe vibration of the linear vibration motor in response to a differencebetween the first frequency and the frequency of the vibration of thelinear vibration motor.

An embodiment of the circuit may be configured to determine an intensityof the vibration of the linear vibration motor and to terminate formingthe drive current in response to the intensity of the vibration beingless than a vibration threshold value.

In an embodiment, the circuit may be configured to not adjust the firstfrequency during other portions of the drive current.

An embodiment of the second circuit may include a resonant frequencysearch circuit configured to estimate a frequency of a back EMF signalreceived from the linear vibration motor.

In an embodiment, the resonant frequency search circuit may beconfigured to measure a time between to two negative to positive zerocrossing transitions of the back EMF signal and estimate an eigenfrequency of the linear vibration motor.

The circuit may have an embodiment that may include a detector circuitconfigured to receive the back EMF signal from the linear vibrationmotor, and includes a zero crossing circuit configured to detect zerocrossings of the back EMF signal.

Those skilled in the art will appreciate that a method of forming asemiconductor device may comprise:

configuring a circuit of the semiconductor device to form a drive signalto form a drive current to apply to a linear vibration motor;

configuring the circuit to form an estimate of an eigen frequency of thelinear vibration motor;

configuring the circuit to form the drive signal at a drive frequencyand a first phase and configuring the circuit to adjust the drivefrequency to a first frequency that is substantially the estimate of theeigen frequency of the linear vibration motor; and

configuring the circuit to form an anti-drive signal at an anti-drivefrequency and a second phase that is substantially opposite to the firstphase, and configuring the circuit to adjust the anti-drive frequency ofthe anti-drive signal to another frequency that is substantially theestimate of the eigen frequency of the linear vibration motor.

An embodiment of the method may include configuring the circuit estimatethe eigen frequency for each cycle of the anti-drive signal and toadjust the anti-drive frequency for each cycle of the anti-drive signal.

In another embodiment the method may include configuring the circuit toselectively enable adjusting the drive frequency to substantially theestimate of the eigen frequency for a first number of cycles of thedrive signal and to form the drive frequency at a substantially constantfrequency for a second number of cycles of the drive signal wherein thesecond number of cycle is subsequent to the first number of drivecycles.

An embodiment may include configuring a counter to count cycles of drivesignal to determine the first and second number of drive cycles.

Another embodiment may include configuring the circuit to selectiveenable the circuit to estimate the eigen frequency in response toforming the anti-drive signal.

In an embodiment, the method may include configuring the circuit tomeasure a time between multiple zero crossings of a back EMF signalreceived from the linear vibration motor.

The method may have an embodiment may include configuring the circuit toreceive a back EMF signal from the linear vibration motor.

An embodiment may include configuring the circuit to measure the timebetween multiple zero crossings of the back EMF signal and use the timebetween multiple zero to estimate the eigen frequency of the linearvibration motor.

An example of an embodiment of a semiconductor device having a circuitmay comprise:

a first circuit configured to form a drive signal to form a drivecurrent to a linear vibration motor;

an output configured to receive a BEMF signal from the linear vibrationmotor;

a second circuit coupled to the receive a signal that is representativeof the BEMF signal and to form an estimate of an eigen frequency of thelinear vibration motor;

the first circuit configured to form the drive signal at a drivefrequency and a first phase and to adjust the drive frequency to a firstfrequency that is substantially the estimate of the eigen frequency ofthe linear vibration motor; and

a stop control circuit configured to form an anti-drive signal at ananti-drive frequency and a second phase that is substantially oppositeto the first phase, wherein the first circuit adjusts the anti-drivefrequency of the anti-drive signal to another frequency that issubstantially the estimate of the eigen frequency of the linearvibration motor.

In view of all of the above, it is evident that a novel device andmethod is disclosed. Included, among other features, is forming acontrol circuit to control the LRA to operate in a closed loop run mode,followed by an open loop run mode, and a break mode where in thefrequency of the signal in the break mode is adjusted. Using the openloop run mode for a portion of the time that the LRA is driven tovibrate assist in minimizing the chance that the weight with the case ofthe LRA thereby reducing audible noise. Additionally, operating in theopen loop run mode reduces the circuitry of a control circuit therebyminimizing cost. Using adjusting the frequency of the anti-drive signalin the break mode assist in operating the break mode with a frequencythat is near to the design frequency of the LRA which may reduce theamount of time required to stop the vibration of the LRA.

While the subject matter of the descriptions are described with specificpreferred embodiments and example embodiments, the foregoing drawingsand descriptions thereof depict only typical and non-limiting examplesof embodiments of the subject matter and are not therefore to beconsidered to be limiting of its scope, it is evident that manyalternatives and variations will be apparent to those skilled in theart. As will be appreciated by those skilled in the art, the exampleform of circuit 100 and circuit 200 and are used as a vehicle to explainthe operation method of the brake mode and the sequence of a method thatoperates the in a closed loop run mode, followed by an open loop runmode, followed by the break mode wherein the frequency of the anti-drivesignal is adjusted. Those skilled in the art will appreciate that thecircuitry that implements the method may have different embodiments thenthe circuitry of detector 130, circuit 140, and the detailed circuitryarrangement of circuit 110.

As the claims hereinafter reflect, inventive aspects may lie in lessthan all features of a single foregoing disclosed embodiment. Thus, thehereinafter expressed claims are hereby expressly incorporated into thisDetailed Description of the Drawings, with each claim standing on itsown as a separate embodiment of an invention. Furthermore, while someembodiments described herein include some but not other featuresincluded in other embodiments, combinations of features of differentembodiments are meant to be within the scope of the invention, and formdifferent embodiments, as would be understood by those skilled in theart.

The invention claimed is:
 1. A semiconductor device including a circuit for controlling a linear vibration motor comprising: a first circuit configured to form a drive signal to control a frequency of a drive current through the linear vibration motor; a second circuit configured to selectively measure a first frequency of a vibration of the linear vibration motor; the circuit configured to operate in a closed loop run mode and form the drive current at a first frequency to cause the linear vibration motor to vibrate, the circuit configured to adjust the first frequency to a second frequency that is substantially the frequency of the vibration of the linear vibration motor in response to a difference between the first frequency and the frequency of the vibration of the linear vibration motor; the circuit configured to operate in the closed loop run mode for a first number of cycles of one of the drive current or the drive signal; the circuit configured to operate in an open loop run mode for a second number of cycles of one of the drive current or the drive signal in response to an end of the first number of cycles, the circuit configured to form the drive current at a substantially fixed frequency for the second number of cycles, the drive current having a first phase; and the circuit configured to operate in a brake mode and to form the drive current with a second phase that is opposite to the first phase in response to expiration of the second number of cycles, the circuit configured to selectively measure a second frequency of a vibration of the linear vibration motor while operating in the brake mode, to form the drive current with a third frequency and to adjust the third frequency to be substantially the second frequency of the vibration of the linear vibration motor.
 2. The circuit of claim 1 wherein the circuit is configured to selectively disable the second circuit and to not measure the frequency of the vibration of the linear vibration motor in response to the end of the first number of cycles of the drive current.
 3. The circuit of claim 2 wherein the circuit is configured to selectively enable the second circuit and to measure the frequency of the vibration of the linear vibration motor in response to the end of the second number of cycles.
 4. The circuit of claim 1 further including a counter configured to count cycles of the drive signal, wherein the circuit is configured to selectively enable operation in the open loop run mode in response to the counter counting the first number of cycles.
 5. The circuit of claim 4 wherein the circuit is configured to selectively enable operation in the brake mode in response to the counter counting the second number of cycles.
 6. The circuit of claim 4 wherein the circuit is configured to selectively terminate operation in the brake mode in response to the counter counting a third number of cycles.
 7. A circuit for controlling a linear vibration motor comprising: a first circuit configured to form a drive signal to control a frequency of a drive current through the linear vibration motor to cause a vibration of the linear vibration motor, the drive current having a first phase; a second circuit configured to selectively measure a frequency of a vibration of the linear vibration motor; and the circuit configured to form the drive current with a first frequency and a second phase that is opposite to the first phase to slow the vibration of the linear vibration motor, the circuit configured to selectively enable the second circuit to measure the frequency of the vibration of the linear vibration motor and to adjust the first frequency to a third frequency that is substantially the frequency of the vibration of the linear vibration motor in response to a difference between the first frequency and the frequency of the vibration of the linear vibration motor.
 8. The circuit of claim 7 wherein the circuit is configured to determine an intensity of the vibration of the linear vibration motor and to terminate forming the drive current in response to the intensity of the vibration being less than a vibration threshold value.
 9. The circuit of claim 7 wherein the circuit is configured to not adjust the first frequency during other portions of the drive current.
 10. The circuit of claim 7 wherein the second circuit includes a resonant frequency search circuit configured to estimate a frequency of a back EMF signal received from the linear vibration motor.
 11. The circuit of claim 10 wherein the resonant frequency search circuit is configured to measure a time between to two negative to positive zero crossing transitions of the back EMF signal and estimate an eigen frequency of the linear vibration motor.
 12. The circuit of claim 10 wherein the circuit includes a detector circuit configured to receive the back EMF signal from the linear vibration motor, and includes a zero crossing circuit configured to detect zero crossings of the back EMF signal.
 13. A method of forming a semiconductor device comprising: configuring a circuit of the semiconductor device to form a drive signal to form a drive current to a linear vibration motor; configuring the circuit to form an estimate of an eigen frequency of the linear vibration motor; configuring the circuit to form the drive signal at a drive frequency and a first phase and configuring the circuit to adjust the drive frequency to a first frequency that is substantially the estimate of the eigen frequency of the linear vibration motor; and configuring the circuit to form an anti-drive signal at an anti-drive frequency and a second phase that is substantially opposite to the first phase, and configuring the circuit to adjust the anti-drive frequency of the anti-drive signal to another frequency that is substantially the estimate of the eigen frequency of the linear vibration motor.
 14. The method of claim 13 including configuring the circuit estimate the eigen frequency for each cycle of the anti-drive signal and to adjust the anti-drive frequency for each cycle of the anti-drive signal.
 15. The method of claim 13 including configuring the circuit to selectively enable adjusting the drive frequency to substantially the estimate of the eigen frequency for a first number of cycles of the drive signal and to form the drive frequency at a substantially constant frequency for a second number of cycles of the drive signal wherein the second number of cycle is subsequent to the first number of drive cycles.
 16. The method of claim 15 including configuring a counter to count cycles of the drive signal to determine the first and second number of drive cycles.
 17. The method of claim 13 including configuring the circuit to selective enable the circuit to estimate the eigen frequency in response to forming the anti-drive signal.
 18. The method of claim 13 including configuring the circuit to measure a time between multiple zero crossings of a back EMF signal received from the linear vibration motor.
 19. The method of claim 13 including configuring the circuit to receive a back EMF signal from the linear vibration motor.
 20. The method of claim 19 including configuring the circuit to measure the time between multiple zero crossings of the back EMF signal and use the time between multiple zero crossings to estimate the eigen frequency of the linear vibration motor. 